1. Field of the Invention
The invention lies in the field of electronic communications. The invention relates to a method for rigid body discovery and peer-to-peer ranging in a scatternet and a communications node executing the method.
2. Description of the Related Art
Precision location based on the peer-to-peer ranging is one of the fundamental attributes of a sensor network that is capable of delivering position dependent information. Such a ranging technique is limited by how the logical topology is constructed during formation of a network. Specifically, when using a sequentially progressive approach to form a scatternet, a logical structure of a spanning tree forms. Such a configuration prohibits direct communication between some of the members in different piconets, in other words, communication is restricted from nodes that are in physical proximity to one another, but that are not members of the same piconet. Therefore, while the range measurements on the piconets physically exist, logically prohibited links will present a significant challenge to the applicability of location algorithms based on peer-to-peer ranging. Another different aspect of the problem of peer-to-peer ranging lies in an availability of reference nodes in a determination of absolute locations in a scatternet.
A scatternet is a network entity made up of connected piconets. It forms in a spanning tree structure as the result of sequentially attaching new piconet onto existing piconet(s) through special kind of members of previous piconets, these members being defined as a slave piconet controller. Extending communications coverage from a first piconet to a second piconet that is within the range of the first piconet is referred to as a hop. When extending a first piconet to the second, or subsequent, hop using a sequential procedure in a spanning tree structure, the piconet controllers are within range of one another and, therefore, a member node can be converted into a slave piconet controller such that a child piconet is formed and is attached to the parent piconet. In such a case, the entity formed by the connected piconets, or what is referred to as a scatternet, forms the spanning tree structure.
A mesh structure can form if a new piconet is attached to the previous ones through shared member nodes or border nodes located at the overlapping area. When there is no border node available, a mesh can form through edge nodes each located in a respective piconet and within range of one another. Accordingly, a “hop” as it is referred to above, is not a single communications span between two nodes in range of one another. Instead, a hop is defined as the communications link between a first piconet controller, an edge node in range of the first piconet controller, an edge node in range of a second piconet controller, and, finally, the second piconet controller. This case illustrates the formation of a scatternet having a mesh format. A significant concern in such a configuration is the spanning tree type of scatternet. Such a configuration prohibits direct communication between the members in different piconets. Therefore, while the range measurements on these piconets physically exist, logically prohibited links present the aforementioned challenge to the applicability of location algorithms based on peer-to-peer ranging.
The definition of a piconet is a basic unit, sometimes being the smallest component of the network. A piconet has member nodes served by a piconet controller (“PNC”), which also can be referred to as a master node under the Bluetooth standard (IEEE 802.15.1; and which is also referred to as a cell under this standard). The peer-to-peer ranging between PNC and member nodes, and amongst the member nodes themselves, can be scheduled and controlled by the PNC. But ranging between nodes on a different branch or different piconets is prohibited.